The introduction
With the development of economy, the pace of urban and rural distribution network construction is accelerated. Due to the limitation of land resources and the cost of development and construction, high-rise residential buildings are the majority of urban construction. Distribution rooms are generally built in the basement of high-rise residential buildings, so the problem of transformer noise becomes the focus of residents' attention.
Due to the performance of amorphous alloy transformers beyond all kinds of silicon steel transformers, both energy-saving and economic [1], its remarkable feature is very low no-load loss, in line with the requirements of national industrial policy and power grid energy saving and consumption reduction.
And has the advantages of stability, safety and fire resistance, the use cost is more economic, in the city's party and government organs, government office buildings, residential areas and other places have been widely used;
However, in practical application, the amorphous alloy dry type transformer has serious noise pollution due to its own vibration and resonance with the surrounding medium. The complaints caused by the noise of dry-type transformers are also increasing, which has become a social problem of wide concern. Therefore, how to effectively reduce the noise pollution of amorphous alloy dry transformer has become an urgent problem to be solved.
1 Noise status and analysis
The amorphous alloy dry-type transformer has both energy saving and economy, and can be popularized and used in the newly built community. In order to save ground space, developers will design power distribution room close to residential buildings or placed underground negative one layer, power distribution room design can be divided into a total wall type and independent power distribution room, so the noise of the dry transformer is easy to pass through the wall or corridor to the living place of residents, causing noise pollution.
1.1 National standard for environmental noise
"City regional environmental noise standards of the People's Republic of China" provisions of the highest city of 5 kinds of regional environmental noise limit, apply the standard of residential area as part of the Ⅰ area.
The area does not exceed 55dB during the day and 45dB at night. Normal people can accept the sound pressure level of 15~45dB. When the noise transmitted by the equipment in the distribution room to the adjacent room exceeds the standard requirements, it will interfere with the normal life and rest of residents.
1.2. Main Causes and Analysis of Noise
The form of noise generated by amorphous alloy dry type transformer is very complex, and there are mainly the following:
(1) The electromagnetic noise of the amorphous alloy dry transformer belongs to the mechanical noise, which is mainly caused by the vibration of the transformer core, winding and magnetic shielding.
The main mechanism of the noise is that the alloy steel sheet of the transformer core vibrates due to magnetostriction under the action of periodic alternating magnetic field, resulting in vibration and noise.
Magneostriction is that the size of the amorphous alloy steel sheet along the magnetic force line direction should increase when the iron core is excited, and the size of the amorphous alloy steel sheet should shrink in the direction of the magnetic force line vertically. Magneostriction makes the magnetic force attract the iron core with the change of the excitation frequency, which mainly appears between the edge of the iron core and the joint of the iron.
However, due to the particularity of amorphous materials, the amorphous alloy core can not be pressed too tightly with clips, so the vibration of the amorphous alloy core is less constrained, the vibration magnitude is larger than that of other materials, and the corresponding noise radiated outward by the vibration of the amorphous alloy core and the coil is larger. In addition, electrified in the dry transformer, wire, iron core under the action of eddy current, radiation out of the noise is far more complex than the noise generated by a single frequency vibration.
(2) When the dry-type transformer is running, the vibration of the iron core will propagate to the surrounding through the foundation and adjacent building structures, and may induce structural noise [2]. The vibration of the iron core causes the vibration of the transformer structure and the supporting device to form resonance, causing additional noise radiation, and sometimes even the source of the main noise.
(3) transformer installation is not stable, the operation process will also produce vibration, so as to amplify the noise caused by the transformer itself and its surrounding factors. The busbar connected by the transformer and the distribution cabinet must pass through a large current. The vibration of the busbar caused by the leakage magnetic field also causes the overall vibration of the transformer busbar bridge to produce noise.
1.3 Path of noise propagation
The noise generated by the vibration of the dry-type transformer in indoor operation is transmitted mainly through three ways:
(1) Air noise. The vibration of the transformer and the base directly radiates the noise into the air through its surface, and the air is mainly used as the medium for transmission.
(2) Primary solid noise. The vibration of the transformer, base and other equipment is transmitted to the structure through the base, and the noise is radiated outward through the surface of the structure, which is the primary solid noise.
(3) Secondary solid noise. Transformers and their equipment generate vibration to radiate air noise to the surrounding, and the pressure wave of air noise again excites the structural parts such as equipment mechanism and houses to make the structural parts vibrate, and then radiate noise outwards from the surface of the structure, which is secondary solid noise.
Through a lot of investigation and research on the structure and surrounding environment of the power distribution room in the community, the noise of amorphous alloy dry-type transformer is transmitted to users in the building by the following ways:
Transformer vibration is transmitted to the foundation through the equipment, and then transmitted to the indoor residents through the wall, column, floor and other structures, and the indoor walls and floor surface radiates a solid noise outward.
The air acoustic pressure wave in the power distribution room directly excite the vibration of the wall and floor and causes noise and sound waves. The air sound in the distribution room is diffracted through the doors and Windows, exhaust vents, pipelines and holes, and then spread to the indoor residents through the doors and Windows and other holes.
Through the above analysis, the noise reduction technology can be divided into active noise reduction and passive noise reduction. Active noise reduction is to reduce the inherent noise of the dry transformer by changing the structure of the dry transformer. At present, it needs to be promoted by the manufacturer of the dry transformer, and can not be implemented as an operation unit. Therefore, passive noise reduction has become an important way to reduce the noise of dry-type transformer, that is, the effect of noise reduction is achieved by weakening and cutting off the above noise propagation path [3].
2. Main measures to reduce the noise of dry-type transformer
According to the different ways of noise transmission of dry power transformer, noise partition is divided into air sound partition and solid sound partition, so solid sound partition and air partition can be used in two ways to reduce noise.
2.1. Noise of air partition dry transformer
The muffler is usually used to eliminate the noise of air partition. The muffler allows the airflow to pass and prevents the noise. It is one of the important measures to eliminate the noise of air power.
Through distribution or box-type transformer installation soundproof door, installed in ventilation shutters, transformer room in the form of ventilation muffler and air partition noise, so as to achieve the air partition noise, reduce the purpose of dry type transformer noise pollution, but only use this way to overcome the noise of the transformer structure and wall body resonance due.
2.2. Solid partition dry-type transformer noise
The vibration of the transformer itself and the vibration conduction to the ground and the surrounding environment can be reduced by installing shock absorbers and connecting the transformer windings with the bus of the low-voltage cabinet. This method can reduce the noise generated by the vibration of the dry transformer, and it is also conducive to reducing the vibration of the transformer broadcast to the foundation, and then the vibration caused by the structure of the wall, column, floor, etc., so as to reduce the noise generated by the vibration of the dry transformer.
The lower part of the dry type transformer is installed with a plurof shock absorbers connected with the concrete foundation arranged on the ground and fixed on the ground; The winding of the dry transformer is connected with the bus bar of the low voltage cabinet by a soft connection. The lower part of the dry transformer is installed with 6 shock absorbers and distributed on the ground, the shock absorber in the installation of each support point is located in the same horizontal plane height;
In addition, channel steel is arranged under the dry type transformer, and the shock absorbers are connected into small units that can increase the stability, so as to achieve the purpose of increasing the overall stability of the system. The load bearing of each shock absorber should be equal as far as possible. Because the weight distribution of the transformer is not uniform before and after the transformer, the center of gravity of the transformer should be located correctly to ensure that the compression amount of each unit shock absorber is basically the same, which is conducive to prolonging the service life of the shock absorber and enhancing the effect of noise reduction.
3. Implementation effect
The noise reduction of amorphous alloy dry-type transformer in the distribution room of a residential area in Jiaxing was carried out by adding shock absorber and combining with muffler.
The 14 floors of the community are as high as 33 floors. The power distribution room is located in the subterranean layer of the community. The power distribution room is directly above the residential floor, building 14, room 101, unit 1.
Produced by a transformer company in Tianjin, the capacity of the transformer is 1250 kVA, the rated voltage is 10kV, the weight of the transformer is 4070 kg. The transformer is modified by adding shock absorber to the transformer base.
3.1 Noise situation of distribution room before transformation
In order to compare the effects before and after the transformation, the master bedroom and bathroom of Room 101, Unit 1, Building 14 of the community were selected as the measurement points to measure the noise before the transformation. The changes in noise size were measured according to the resonant frequencies emitted by the transformers in the distribution room. The measurement results are shown in Table 1.
By measuring the bottom acceleration of No. 1 and No. 2 transformers in the distribution room, the measurement results are shown in Table 2.
As can be seen from Table 1, when the resonant frequency of the transformer is between 16 and 31.5 Hz, the noise emitted by the transformer is more than 45dB when measured in the bedroom and the sanitation, which seriously exceeds the relevant requirements stipulated by the state at night and seriously affects the life of the residents.
After reducing the noise of the dry-type transformer by adding shock absorbers to the transformer base, noise measurement was carried out on the original measurement points again. The results are shown in Table 1 and Table 2. Compared with the measured results before and after the transformation, it is found that the noise and the bottom acceleration of the transformer at the corresponding frequency are significantly reduced, and the effect of noise reduction measures is very obvious.
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